This invention relates in general to oscillator circuits and in particular to a low power oscillator which combines high start-up ability with low power consumption.
The output of an oscillator circuit is used to drive any of a variety of devices. For this purpose, it is desirable for the oscillator output to provide stable signals of sufficient amplitude and for the oscillator output to reach such state as soon as possible to minimize the time one must wait before the oscillator output can be used to drive different devices. Hence it is in general desirable for oscillator circuits to have high start-up ability.
One way to achieve good start-up ability is to employ a high gain, high power driver for driving the oscillator output, where the driver usually entails larger device geometries. While the high gain, high power driver ensures good start-up ability even with higher resistance crystals or resonators, such drivers will also cause a larger current in the circuit and consumes more power. Furthermore, even after the oscillator has completed its start-up cycle to achieve a stable output, the high gain, high power driver tends to distort the output waveform. The distorted output waveform creates harmonics in the signal and can cause electromagnetic interference with other electronics components. In order to avoid the undesirable effects of using high gain, high power drivers, circuit designers may prefer lower gain, lower power drivers with poorer start-up ability. In other words, circuit designers are forced to compromise in choosing between characteristics of high gain, high power drivers with good start-up ability on the one hand and lower gain, lower power drivers with poor start-up ability. It is therefore desirable to provide oscillator circuits with both high start-up ability and low power consumption.